After completion of standard treatment, pts with aggressive CD20+ B-cell lymphoma and mantle cell lymphoma were randomized to either observation or maintenance therapy with rituximab (375 mg/m2) administered every 3 months for 2 years. Both pts after first line therapy and pts after relapse treatment were included in the study. Pts with aggressive lymphoma were enrolled if they had achieved a complete response (CR) after initial treatment. Pts with aggressive lymphoma with residual tumor mass underwent positron emission tomography (PET) and qualified for randomization if this examination showed no signs of tumor activity. Pts with mantle cell lymphoma were eligible for the study if at least a partial response (PR) was achieved. Primary endpoint of the study was progression free survival (PFS), secondary endpoints were time to progression (TTP), overall survival (OS) and response to treatment. Differences between PFS and OS were analysed using the logrank test and the proportional hazard model of Cox. TTP was analyzed using a competing risk model with death as competing event.